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Elasticity vs Plasticity

Physics | 7-14 yrs | Animation

All of you would have heard the terms ‘plastic’ and ‘elastic’. Do you know that ‘plastic’ and ‘elastic’ are also important scientific terms that are used to describe the properties of materials such as rubber, plastic, metal, etc?

What is elasticity?

In Physics, when an external force is applied to the surface of any material, the material goes through a physical change or deformation. When the force is removed, the material, depending on its properties, may or may not return to its original shape. Now, if the material returns to its original shape, it is said to be elastic in nature, and this property is known as ‘elasticity’.

What is plasticity?

On the other hand, if the material does not regain its original shape, it is said to be plastic in nature, and this property is known as ‘plasticity’.

What kind of materials are known as elastic and plastic materials?

Elastic material:

One of the most common examples of elasticity is a rubber band. You can easily stretch it to a length many times its original one, but when you release it, it returns to its original shape. The balloons that you use in your birthday parties are again made of rubber, which is an elastic material. Even those stretchable jeans and shirts that you wear are made of an elastic material, mostly spandex which is a stretchable fiber.

Plastic material:

The bending of a steel rod upon applying force is an example of plasticity. Once bent, it cannot come back to its original position.

What happens when force is applied to a body?

When an external force is applied to a body, the body tends to break. This happens because the distance between the atoms inside it, increases and each atom tries to pull its neighboring atom closer to itself. The pull between the atoms creates a force inside the body that tries to resist the deformation. This force is called strain, and the deforming force on the body is known as stress. The resistance of a material to elastic deformation or deflection is called stiffness. Also, there is a limit to the force which a body can resist without breaking. This limit is called the elastic limit of a body.

Difference between plasticity and elasticity

Plasticity

Elasticity

Process

It is an irreversible process.

It is a reversible process.

Ductility

Plastic materials are highly ductile in nature.

Elastic materials are less ductile in nature.

Shape and size

The shape and size of materials change permanently in this process.

The shape and size of materials does not change permanently

Example

Plastic

Rubber

Hooke’s Law and elasticity

Hooke’s Law proposes that the amount of elongation of a spring is directly proportional to the force that is acting on it. Springs and every elastic material require an application of some force to stretch it. The force required to stretch an elastic material depends on the stiffness of the material, and is known as the ‘Young’s modulus’ or ‘elastic modulus.

In other words, Young’s modulus is a measure of the flexibility of a given material. With the help of Young’s modulus, engineers and scientists can calculate and understand the behavior of a material under load. For example, it can be used to foretell how much a wire will extend under tension, or to predict the load at which a thin column will give away under compression.

Young’s modulus is constant over a range of strains. Such materials are called linear. Examples of linear materials include Steel, Carbon Fiber and Glass.
Rubber is a non – linear material.

Uses of plasticity in the metal industry

The metal industry takes advantage of the plastic properties of materials by making them undergo some degree of permanent deformation without rupture or failure. Almost all materials including metals, plastics, soils, rocks and concrete undergo plastic deformations. Heat and pressure are commonly used to shape these materials into the desired form. This is done in a carefully controlled environment so that the objects do not beak apart. Metals like copper, silver, steel and gold have greater plastic deformation ranges. Materials like rubber, crystals and ceramics have the least plastic deformation ranges.

5 Interesting facts about elasticity

  1. A steel bar or wire can be extended only around 1 percent of its original length, while in case of rubberlike materials, we can get elastic extensions of up to 1,000 percent also.
  2. When force is applied on a given body, the bonds between the atoms inside it break leading to deformations. Elastic materials like rubber have long-chain molecules that uncoil because of which it gets extended and gets back into shape when they recoil.
  3. Rubber can be stretched three times its original size.
  4. Your hairs have elastic properties too. A single strand of hair can hold 100 grams of weight without breaking!!
  5. Young’s modulus is represented by the alphabet E. The higher this value is, the stiffer the material is!!
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